MicroRNA-99b-5p downregulates protein synthesis in human primary myotubes

Area of Science:

• Molecular Biology
• Cellular Biology
• Muscle Physiology

Background:

• MicroRNAs (miRNAs) are key regulators of gene expression and cellular homeostasis.
• Previous research indicated an age-dependent link between microRNA-99b (miR-99b-5p) and reduced muscle protein synthesis.
• The mammalian target of rapamycin (MTOR) pathway is crucial for regulating protein synthesis.

Purpose of the Study:

• To investigate the role of miR-99b-5p as a negative regulator of protein synthesis in human muscle cells.
• To determine if miR-99b-5p targets the MTOR signaling pathway.
• To explore the impact of miR-99b-5p on MTOR signaling components.

Main Methods:

• Overexpression of miR-99b-5p in human primary myotubes from young and old donors.
• Confirmation of miR-99b-5p binding to the MTOR 3'-untranslated region (UTR) in C2C12 myoblasts.
• Analysis of MTOR pathway components, including MTOR protein and RPTOR.

Main Results:

• Overexpressing miR-99b-5p significantly decreased protein synthesis in human myotubes, irrespective of donor age.
• Direct binding of miR-99b-5p to the MTOR 3'-UTR was confirmed.
• The reduction in protein synthesis correlated with decreased RPTOR levels, not MTOR protein suppression.

Conclusions:

• MicroRNA expression modulation can regulate protein synthesis in human muscle cells.
• miR-99b-5p acts as a negative regulator of protein synthesis by inhibiting MTOR signaling, specifically impacting RPTOR.
• This provides a potential molecular mechanism contributing to age-related muscle wasting (sarcopenia).